This invention relates generally to systems for generating speed-proportional signals, and more particularly, to a system for generating a speed-proportional voltage having an incremental position transmitter which provides two transmitter voltages which are shifted in the positive or negative direction with respect to one another by 90.degree., depending upon the direction of rotation, the voltage having a speed-independent amplitude.
Incremental position transmitters of the type which provide two transmitter voltages shifted by 90.degree. in the positive or negative direction, depending upon the direction of rotation, are commercially available. Such position transmitters contain a disc which is connected to a rotating part, the disc having markings distributed along its circumference. The disc is scanned optically, or inductively, so that a pulse sequence is formed having a frequency which is proportional to the speed of the rotating part. However, the amplitude of the pulses is independent of the speed. Information pertaining to the position of the rotating part is obtained by counting the pulses. If the pulse sequence is coupled to a frequency-voltage converter, a signal at the output of the converter is obtained which corresponds to the speed of the rotating part. In the known systems, a relatively large number of pulses must be evaluated in order to determine the speed, and therefore the speed signal reacts with considerable delay to variations in the actual speed of the rotating part. This delay produces a disturbing effect in the operation of speed control circuits.
Three-phase tachometer generators are frequently used for measuring speed. The tachometer generators produce a voltage having an amplitude which is proportional to the speed of the tachometer generator. Diodes having predetermined threshold voltages are generally required for rectifying the three-phase current; the threshold voltage producing a disturbing effect especially at low speeds. Since the rectified signal of the three-phase tachometer generator does not produce a signal polarity which is responsive to the direction of rotation, complicated additional measures for determining the direction of rotation from the phase sequence of the three-phase current are necessary. The foregoing disadvantges are avoided, however, by utilizing a DC tachometer generator which supplies a DC voltage having an amplitude which is proportional to the speed, the DC voltage having a polarity which is independent of the direction of rotation. It is a problem with such DC tachometer generators, however, that the electromechanical commutator which is required exhibits relatively rapid wear. Both kinds of tachometer generators have the further disadvantage that no position information can be derived from their output signals. A position generator is therefore required in addition for determining the position of the rotating part.
It is, therefore, an object of this invention to provide a method for generating a speed-proportional voltage wherein the reaction time to variations in speed is small.
It is a further object of this invention to provide an apparatus for producing a speed-proportional voltage which exhibits short reaction times to variations in the speed of the rotating part if the apparatus is used in incremental position transmitters.